W. Liang, Y. Huang, Y. Xu, R. K. Lee and A. Yariv: “Highly Sensitive Fiber Bragg Grating Refractive Index Sensors”, Appl. Phys. Lett. 86, 151122 (2005) discloses a fiber-optic sensor which contains a Bragg grating. The fiber-optic sensor contains an optical waveguide having a core and a cladding, the cladding being removed in the Bragg grating region. The sensor can be immersed into gases or liquids, the Bragg wavelength reflected by the Bragg grating changing in accordance with the index of refraction or the refractive index of the medium surrounding the sensor.
However, a drawback of this sensor is the low resolution thereof. The Bragg wavelength will merely change by fractions of a nanometer when the refractive index changes. As a result, highly complex light sources and spectrometers are required to determine the wavelength shift and the resulting refractive index of the medium.